fix: review fixes for the metric template and the radial constraint

A new drawing (#1441) recorded ISO-25 as the current dimension style by
name only. Every other place that changes it sets the header's handle as
well, and a DWG carries the current style by handle alone, so a saved new
drawing reopened on Standard. The style's handle now comes back from the
helper that adds it.

A radius constraint (#1443) anchored the circle's centre from the shape of
its references — one whole entity — but a single whole reference is also a
line's length, whose start is what stays. The entity decides now.

The two tests that encoded the replaced rules follow them: a negative
radius validates by its magnitude, as a negative distance already did, and
only zero is refused; a new drawing's dimension text reads at ISO-25's
comma separator.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/scene/parametric_constraints.rs

@@ -732,8 +732,15 @@ pub(crate) fn dimensional_anchor_refs(
         return Vec::new();
     };
     // A whole circle or arc (a radius or diameter): its center stays and the
-    // value resizes it.
-    if refs.len() == 1 && first.marker.is_none() {
+    // value resizes it. A single whole reference can also be a line's length,
+    // whose start is what stays, so the entity decides.
+    if refs.len() == 1
+        && first.marker.is_none()
+        && matches!(
+            document.get_entity(first.entity),
+            Some(acadrust::EntityType::Circle(_) | acadrust::EntityType::Arc(_))
+        )
+    {
         return vec![ParametricRef::center(first.entity)];
     }
     // Three point references: a three-point angle `[first, vertex, second]`.